Propylene-based polymers and copolymers are well known in the art for their usefulness in a variety of applications, including the manufacture of nonwoven fabrics. Such fabrics have a wide variety of uses, such as in medical and hygiene products, clothing, filter media, and sorbent products. Meltblown nonwoven fabrics are particularly useful in hygiene products, such as baby diapers, adult incontinence products, and feminine hygiene products. An important aspect of these fabrics, particularly in hygiene applications, is the ability to produce aesthetically pleasing fabrics having good leakage performance at a low cost. Good leakage performance is achieved via the elasticity of the elastic layers of the fabrics, which provides better fit and conformity to the wearer, resulting in fewer leaks.
Production of meltblown nonwoven fabrics using commercially available propylene-based polymers having a melt flow rate (MFR) less than 25 g/10 min in the elastic layers can be difficult, because the low MFR of such polymers requires high melt temperatures and high pressures to melt blow. High process temperatures can cause undesirable degradation in the extruder, while high pressures limit the throughput rate of the melt blowing equipment. Previously, some propylene-based polymers have been blended with an additional polymer or polymers post-reactor, often isotactic propylene homopolymers, and then visbroken with peroxide to achieve a higher MFR polymer for use in elastic layers. Blending with an additional polymer, however, typically increases manufacturing cost and reduces the elastic performance of the resulting nonwoven fabrics. Similarly, visbreaking also increases manufacturing costs and adds complexity to manufacturing processes.
It is therefore desirable to form the elastic layers of meltblown nonwoven fabrics from propylene-based polymers having a higher MFR (i.e., greater than 25 g/10 min) without blending the propylene-based polymers post-reactor with homopolypropylene or other polymers and without visbreaking the polymers. Such fabrics can be produced under broader process conditions, and at higher throughput rates and lower costs.
U.S. Patent Application Publication No. 2002/0019507 describes propylene-based polymers that have been visbroken with peroxide to increase the MFR of the polymer for use in adhesive applications.
U.S. Patent Application Publication No. 2005/0130544 describes blends of propylene-based polymers with propylene homopolymers for use in fiber spinning applications.
U.S. Patent Application Publication No. 2008/0172840 describes polyolefin blend compositions suitable for use in spunbond fiber or filament applications having an MFR between 100 and 500 g/10 min.
U.S. Patent Application Publication No. 2009/0124154 describes nonwoven fabrics comprising two or more propylene-based elastomers and one or more propylene-based thermoplastic polymers.
International Publication No. WO 2009/064583 describes nonwoven fabrics made from compositions comprising a low crystallinity propylene-based elastomer, a high crystallinity propylene-based elastomer, and a propylene-based thermoplastic polymer.